This use of optical signals opens up possibilities for sending information at GBit/second rates but this leads to a problem in that current electronic logic is not yet available to separate an incoming optical signal at these bit rates into its component channels.
In accordance with one aspect of the present invention, an optical signal processing system comprises optical demultiplexing means for demultiplexing an n channel time division multiplexed optical input signal to generate n subsidiary optical signals, one for each channel and further comprises a clock signal generator for generating a clock signal with a frequency (B) related to the bit rate of the optical input signal; n optical sampling devices; an optical splitter optically coupled with the optical sampling devices for feeding the optical input signal in parallel to each of the n sampling devices; control means responsive to the clock signal for regularly actuating the sampling devices to pass samples of the optical input signal which constitute the subsidiary optical signals; and delay means whereby the delay means causes the subsidiary optical signals to correspond with respective ones of the n channels.
Preferably the delay means are arranged to enable all channels to be sampled simultaneously.
The system may further comprise n conversion means for converting the subsidiary optical signals into corresponding electrical signals. The conversion means may comprise conventional regenerators.
Where conversion means are provided, the n optical sampling devices will be optically coupled with respective ones of the conversion means.
The optical sampling devices may conveniently comprise optical signal modulators such as electro-optic modulators.
The delay means preferably comprises optical delay means. For example, the delay means may be positioned betwen the optical splitter and the n optical sampling devices to impart different delays to those portions of the optical input signal fed to at least n-1 of the optical sampling devices so that the optical sampling devices can be sampled simultaneously by the control means the delays being chosen such that the portion of each signal which is passed through the sampling devices corresponds to a respective channel. The delay means may for example be provided by different lengths of optical waveguide (such as optical fibre) between the optical splitter and the sampling devices.
In an alternative arrangement, the delay means is non-optical and may be arranged to cause the control means to actuate the sampling devices in succession whereby the optical signals fed to the optical sampling devices are successively sampled.
The delays imparted by the delay means will typically be integral multiples (not necessarily equally spaced) of a time T, where the bit rate of the multiplexed input signal 1/T bit/second.
Preferably, where conversion means is provided the clock signal generator feeds the clock signal to a divide-by-n circuit having an output connected with the conversion means.
Preferably, the clock signal generator is responsive to the optical input signal to determine the bit rate of the optical input signal and to generate a corresponding clock signal.
In accordance with another aspect of the present invention, an optical signal processing system comprises optical demultiplexing means for demultiplexing a 2 channel time division multiplexed optical input signal to generate 2 subsidiary optical signals, one for each channel wherein the demultiplexing means comprise a clock signal generator for generating a clock signal with a frequency related to the bit rate of the optical input signal; and first coupling means having an input port for receiving the optical input signal and first and second output ports, the coupling means being responsive to the clock signal to connect the input port alternately with the first and second output ports.
It should be understood in this context that by "channel" we include the possibility of there being subsidiary channels within a particular channel. In this situation further coupling means may be connected to each of the output ports of the first coupling means as required to achieve full demultiplexing.